Problem: Expand. If necessary, combine like terms. $(x+5)(x-5)=$
Solution: Notice that this expression has the following special form: $(a+b)(a-b)$ This form expands to what we call "a difference of squares": $( a+ b)( a- b)= a^2- b^2$ Using the above pattern, we get: $\begin{aligned} ( x+ 5)( x- 5)&= x^2- 5^2 \\\\ &=x^2-25 \end{aligned}$